Particularly on the employment aspect.  If people need to be employed continuously, or nearly continuously, to keep their visas, then it gives their employers the ability to control them completely.  

That's horrible, and we shouldn't stand for it.

We shouldn't approve an immigration or guest worker bill unless it gives room for immigrants/guest workers to be unemployed for, say, up to four months of every year.  That would give the immigrant at least some opportunity to say, "if you fire me, I'll just get another job," and have a good chance of doing so before the cops come knocking at their door.